Variable path length spectrophotometric probe

Abstract

A compact, variable pathlength, fiber optic probe for spectrophotometric measurements of fluids in situ. The probe comprises a probe body with a shaft having a polished end penetrating one side of the probe, a pair of optic fibers, parallel and coterminous, entering the probe opposite the reflecting shaft, and a collimating lens to direct light from one of the fibers to the reflecting surface of the shaft and to direct the reflected light to the second optic fiber. The probe body has an inlet and an outlet port to allow the liquid to enter the probe body and pass between the lens and the reflecting surface of the shaft. A linear stepper motor is connected to the shaft to cause the shaft to advance toward or away from the lens in increments so that absorption measurements can be made at each of the incremental steps. The shaft is sealed to the probe body by a bellows seal to allow freedom of movement of the shaft and yet avoid leakage from the interior of the probe.

What is claimed is: 
     
       1. A probe for making spectrophotometric measurements in a fluid with a spectrophotometer and a light source, said probe comprising: a probe body having an interior;   first means for carrying light from said light source to said interior of said probe body, said first carrying means having a first end and a second end;   second means for carrying light to said spectrophotometer from said interior of said probe body, said second carrying means having a first end and a second end;   a shaft, said shaft positioned in said interior of said probe body, said shaft spaced apart from said first and said second carrying means and aligned therewith;   means for moving said shaft;   means for sealing said shaft to said probe body so that fluid does not pass from said interior of said probe body;   means for reflecting light, said reflecting means carried by said shaft;   lens means for directing light received from said second end of said first carrying means to said reflecting means and for directing light received from said reflecting means to said second end of said second carrying means; and   an inlet formed in said probe body and in communication with said probe interior so that said fluid may enter said probe interior; and   an outlet formed in said probe body and in communication with said probe interior so that said fluid may exit said probe interior.   
     
     
       2. The probe as recited in claim 1, wherein said lens means further comprises a collimating lens. 
     
     
       3. The probe as recited in claim 1, wherein said shaft has an end with a surface, said end opposing said lens means, and said reflecting means is a portion of said surface. 
     
     
       4. The probe as recited in claim 1, wherein said moving means further comprises: a motor; and   means for advancing said shaft toward or away from said lens in response to operation of said motor.   
     
     
       5. The probe as recited in claim 4, wherein said shaft has an end with a surface, said end opposing said lens means, and said reflecting means is a portion of said surface, and wherein said moving means further comprises: a motor; and   means for advancing said shaft toward or away from said lens in response to operation of said motor.     
     
     
       6. The probe as recited in claim 1, wherein said first carrying means is a first optical fiber having a first end and an opposing second end, said first end of said first optical fiber receiving light from said light source, said second end of said first optical fiber positioned in said interior of said probe body, said first optical fiber carrying said light from said light source to said second end of said first optical fiber; and wherein said second carrying means is a second optical fiber having a first end and an opposing second end, said second end of said second optical fiber receiving light from said interior of said probe body, said first end in optical connection with said spectrophotometer, said second ends of said first and said second optical fibers positioned so as to be adjacent and coterminous.   
     
     
       7. The probe as recited in claim 6, wherein said lens means further comprises a collimating lens. 
     
     
       8. The probe as recited in claim 6, wherein said shaft has an end with a surface, said end opposing said lens means, and said reflecting means is a portion of said surface. 
     
     
       9. A probe for use with a spectrophotometer and a light source in making spectrophotometric measurements in a fluid, said probe comprising: a probe body having an interior;   a first optical fiber having a first end and an opposing second end, said first end of said first optical fiber receiving light from said light source and said second end of said first optical fiber positioned in said interior of said probe body;   a second optical fiber having a first end and an opposing second end, said second end of said second optical fiber receiving light from said interior of said probe body and said first end in optical connection with said spectrophotometer, said second end of said second optical fiber positioned parallel and adjacent to said second end of said first optical fiber, whereby said first optical fiber carries said light from said light source to said second end of said first optical fiber and said second optical fiber carries said light from said interior to said first end of said second optical fiber;   a shaft, said shaft positioned in said interior of said probe body, said shaft spaced apart from said first and said second optical fibers and aligned therewith;   means for moving said shaft;   means for sealing said shaft to said probe body so that fluid does not pass from said interior of said probe body;   means for reflecting light, said reflecting means carried by said shaft; and   a lens, said lens opposing said reflecting means so that said lens directs light from said second end of said first optical fiber to said reflecting means and from said reflecting means to said second end of said second optical fiber.   
     
     
       10. The probe as recited in claim 9, wherein said sealing means is a bellows. 
     
     
       11. The probe as recited in claim 9, wherein said shaft has an end with a surface, said end opposing said lens means, and said reflecting means is a portion of said surface. 
     
     
       12. The probe as recited in claim 9, wherein said lens is a planoconvex lens having a convex side and a plane side, said convex side facing said second ends of said first and second optical fibers and said plane side facing said reflecting means. 
     
     
       13. The probe as recited in claim 9, wherein said moving means further comprises: a motor; and   means for advancing said shaft toward or away from said lens in response to the operation of said motor.   
     
     
       14. The probe as recited in claim 12, wherein said moving means further comprises: a motor; and   means for advancing said shaft toward or away from said lens in response to the operation of said motor.   
     
     
       15. A probe for use with a spectrophotometer and a light source in making spectrophotometric measurements in a fluid, said probe comprising: a probe body having an interior;   a first optical fiber having a first end and an opposing second end, said first end receiving light from said light source, and said second end transmitting said light into said interior of said probe body;   a second optical fiber having a first end and an opposing second end, said first end in optical connection with said spectrophotometer so that light from said second end of said first optical fiber must travel a distance through said fluid to reach said second end of said second optical fiber, said second end of said second optical fiber receiving light from said interior of said probe body;   a shaft, said shaft positioned in said interior of said probe body, said shaft spaced apart from said first and said second optical fibers and aligned therewith;   means for sealing said shaft to said probe body so that fluid does not pass from said interior of said probe body;   a reflector, said reflector carried by said shaft;   a collimating lens, said lens opposing said reflector so that said lens directs light from said second end of said first optical fiber to said reflector and from said reflector to said second end of said second optical fiber;   a motor; and   means for advancing said shaft toward or away from said lens in response to the operation of said motor.   
     
     
       16. The probe as recited in claim 15, wherein said sealing means further comprises a bellows encircling said shaft, said bellows expanding as said reflecting means moves toward said second ends of said first and second optical fibers and said bellows contracting as said reflecting means moves away from said second ends of said first and second optical fibers. 
     
     
       17. The probe as recited in claim 15, wherein said lens is a planoconvex lens having a convex side and a plane side, said convex side facing said second ends of said first and second optical fibers and said plane side facing said reflecting means. 
     
     
       18. The probe as recited in claim 15, further comprising means for producing pulses, wherein said motor is a linear stepper motor responsive to said pulses. 
     
     
       19. The probe as recited in claim 17, wherein said sealing means further comprises a bellows encircling said shaft, said bellows expanding as said reflecting means moves toward said second ends of said first and second optical fibers and said bellows contracting as said reflecting means moves away from said second ends of said first and second optical fibers; and wherein said shaft has an end with a surface, said opposing said lens means, and said reflecting means is a portion of said surface.